Aftermath

Robb returns from the mission without incident. However, while he was away his key prisoner Ser Jaime Lannister was released by his mother Catelyn Stark without his consent. The betrayal, combined with the ongoing worry about his siblings captivity, causes Robb to seek solace in the arms of Talisa Maegyr, flaunting his vow to marry into House Frey.[4]

In the books

In the A Song of Ice and Fire, novels the Crag surrenders only after losing a battle for control of the castle. Robb is wounded in the battle and shortly afterwards learns of the apparent deaths of his brothers at the hand of Theon Greyjoy. It is this different betrayal that causes him to seek solace in the arms of a woman despite his betrothal, in this case Jeyne Westerling rather than Talisa Maegyr.